Recent studies have shown that employing reconfigurable antennas can improve the gains offered by Multiple Input Multiple Output (MIMO), Single Input Multiple Output (SIMO) and Multiple Input Single Output (MISO) systems as explained in “Design and evaluation of a reconfigurable antenna array for MIMO systems,” IEEE Transactions on Antennas and Propagation, vol. 56, no. 3, 2008, by D. Piazza, N. J. Kirsch, A. Forenza, R. W. Heath Jr., and K. R. Dandekar; “A MIMO system with multifunctional reconfigurable antennas,” IEEE Antennas and Wireless Propagation Letters, vol. 5, no. 31, pp. 463-466, 2006, by B. A. Cetiner, E. Akay, E. Sengul, and E. Ayanoglu; “Multifunctional reconfigurable MEMS integrated antennas for adaptive MIMO systems,” IEEE Communications Magazine, vol. 42, no. 12, pp. 62-70, 2004, by B. A. Cetiner, H. Jafarkhani, Jiang-Yuan Qian, Hui Jae Yoo, A. Grau, and F. De Flaviis; “Maximizing MIMO capacity in sparse multipath with reconfigurable antenna arrays,” IEEE Journal of Selected Topics in Signal Processing, vol. 1, no. 1, pp. 156-166, 200, by A. M. Sayeed and V. Raghavan; and “Two port reconfigurable circular patch antenna for MIMO systems,” Proceedings of the European Conference on Antennas and Propagation, EUCAP, 2007 by D. Piazza, P. Mookiah, M. D'Amico, and K. R. Dandekar. These antennas adaptively change their electrical and radiation properties according to the propagation characteristics of the wireless channel in order to provide a strong channel between the transmitting and receiving antennas in a given communication system.
To optimally use such reconfigurable antennas it is necessary to know the channel response between the transmitter and the receiver for each antenna configuration as shown in “A reconfigurable multiple-input multiple-output communication system,” IEEE Transactions on Wireless Communications, vol. 7, no. 5, 2008, by A. Grau, H. Jafarkhami, and F. De Flaviis. However, estimating the channel response for each antenna configuration at the transmitter and at the receiver as described in the above-mentioned paper has been demonstrated to be power consuming and to have a detrimental effect on the performance of the reconfigurable MIMO, MISO and SIMO systems. The negative effect of channel estimation on the performance of the communication system increases proportionally with the number of antenna configurations, reaching the point where the losses, caused by imperfect channel estimation, may be higher than the capacity gain offered by reconfigurable antennas.
In order to overcome this channel estimation problem, a method is proposed herein that allows both linear and non-linear multi-element reconfigurable antennas to select the antenna configuration at the receiver without any extra power consumption and modifications to the data frame of conventional, non-reconfigurable MIMO, SIMO or MISO systems. This configuration selection scheme does not aim to maximize the throughput for each particular channel realization, but it selects the antenna configuration that, on average, increases the spectral efficiency of the communication link.
The adaptive algorithm presented below is shown to be effective for pattern reconfigurable antennas, though its use can also be extended to other classes of antennas. Pattern reconfigurable antennas are selected because of their advantages in MIMO, SIMO or MISO communications with respect to antennas that exploit space or polarization diversity. Pattern diversity antennas, similarly to polarization diversity antennas, allow system designers to reduce the antenna space occupied on a communication device, solving the size and cost constraints that prevent the antennas from being placed far apart in conventional multi element antenna systems as taught in “Benefit of pattern diversity via two-element array of circular patch antennas in indoor clustered MIMO channels,” IEEE Transactions on Communications, vol. 54, no. 5, pp. 943-954, 2006, by A. Forenza and R. W. Heath Jr.
Also, unlike polarization reconfigurable antennas, pattern reconfigurable antennas can be effectively used without the need for switching antenna configuration at the transmitter and at the receiver simultaneously for polarization alignment. Moreover, pattern reconfigurable antennas, unlike polarization reconfigurable antennas, allow for the generation of an ideal infinitive number of perfectly uncorrelated patterns per antenna element in order to optimally tune the wireless channel for the highest spectral efficiency. A configuration selection scheme is proposed in accordance with the invention that analyzes the performance achievable with reconfigurable circular patch antennas as described in “Two port reconfigurable circular patch antenna for MIMO systems,” Proceedings of the European Conference on Antennas and Propagation, EUCAP, 2007, authored by D. Piazza, P. Mookiah, M. D'Amico, and K. R. Dandekar. As described in the D. Piazza paper, these antennas are capable of dynamically changing their patterns by varying the radius of the circular patch. An analysis of the performance of these Reconfigurable Circular Patch Antennas (RCPAs), in terms of ergodic channel capacity and Bit Error Rate (BER), is conducted using the clustered channel model as taught in “TGn channel models,” IEEE 802.11-03/940r4, 2004 by V. Erceg et al.
Through this approach the array configuration selection is directly linked to i) the spatial characteristics of the wireless channel (angle spread of the power angular spectrum), ii) the levels of pattern diversity existing between the elements of the reconfigurable array, iii) the differences in radiation efficiency and input impedance between the various antenna configurations, and iv) the average system Signal-To-Noise-Ratio (SNR). An antenna selection scheme optimized for multi-element reconfigurable antennas is desirable and is described herein.